Stirrer organ in composite construction

ABSTRACT

The invention relates to a stirrer organ ( 1 ) in composite construction comprised of a metallic part ( 4 ) and a hybrid casting ( 9 ), with the hybrid casting ( 9 ) being fixed to the metallic part ( 4 ) by means of at least one anchoring element which forms at least one back-cutting in the hybrid casting ( 9 ). Furthermore, the present invention relates to a method for rehabilitating a damaged metallic stirrer organ which when applied provides a rehabilitated stirrer organ ( 1 ) in composite construction. The invention tackles the task of creating a stirrer organ ( 1 ) in hybrid construction which features a largest possible metallic part ( 4 ) because higher strength can hereby be achieved. This task is inventively solved in that the anchoring element is provided with a perforated plate ( 5 ) which is spot-wise fastened to the metallic part ( 4 ) and which is arranged at least partly at a small distance to the surface of the metallic part ( 4 ) so as to configure the at least one back-cutting.

The present invention relates to a stirrer organ in compositeconstruction comprised of a metallic part and a hybrid casting, with thehybrid casting being fixed to the metallic part by means of at least oneanchoring element which forms a back-cutting in the hybrid casting.

Furthermore, the present invention relates to a method forrehabilitating a damaged metallic stirrer organ which when appliedprovides a rehabilitated stirrer organ in composite construction.

Stirrer organs of this species are applied in particular for stirring ofcorrosive and/or abrasive media. On account of their extraordinarilyhigh chemical and mechanical stresses, stirrer organs are exposed tosevere wear and tear. Until some years ago, these components weretherefore made of high-alloy corrosion-resistant steel grades. Since itturned out to be impossible to achieve satisfying service life campaignswith these materials, first efforts have been made some time ago tosubstitute steel partly by hybrid castings.

Hybrid casting is to be understood hereunder as a mixture composed of abonding agent and an aggregate. For example, the aggregate is afine-grain wear-resistant and corrosion-proof material, e.g. siliconcarbide, corundum, quartz sand, glass or even blends of these materials.Usable as bonding agents are plastic materials, e.g. epoxy resin, vinylester resin or polymethylmethacrylate (PMMA).

The German utility patent DE 201 11 789 U1 describes a stirrer organ inform of a metallic stirrer blade driven by a stirrer shaft. The end ofthe stirrer blade is provided with a protective cap made of hybridcasting. The protective cap is connected in a form-fit arrangement withthe stirrer blade. To this effect, there are boreholes arranged in thestirrer blade which are interspersed with the hybrid casting when thestirrer blade end is cast around with the hybrid casting.

A disadvantage with this type of a form-fit connection between thehybrid casting and the metallic stirrer blade lies in that the hybridcasting is merely retained spot-wise by the hybrid casting webs arrangedin the boreholes at the stirrer blade. If the hybrid casting is exposedto heavy loads, stress peaks are thus entailed in the area of thecontact points between the borehole and the hybrid casting. The hybridcasting is hereby weakened locally and can be destroyed, whereby thehybrid casting part may at least partly loosen from the metallic stirrerblade.

For anchoring a hybrid casting at a metallic machinery component, it isfurthermore known from DE 29723 409 U1 to utilize usual bolts asanchoring elements which are screwed into the metallic machinerycomponent and the heads of which form back-cuttings in the hybridcasting, whereby a strong cohesion is established between the metallicmachinery component and the hybrid casting.

This solution bears a drawback in that a large quantity of the hybridcasting must be cast in order to completely enclose the bolt heads. Thusthe hybrid casting takes a substantial part of the overall thickness ofthe composite component. Since the overall thickness of the compositecomponent is defined or at least limited by the hydrodynamic task to befulfilled, the metallic part can therefore only have a low materialthickness. However, since the metallic part represents the load-bearingbasis for the composite component, it must be of the highest possiblethickness to the benefit of the necessary strength. Large hybrid castingportions in a composite work piece thus frequently entail problems instrength.

Another drawback of this solution also rests in that the hybrid castingis retained by the bolts merely at certain points and spots. If thehybrid casting is exposed to heavy loads, stress peaks are entailed inthe area of the contact points between the bolt and the hybrid casting.The hybrid casting is hereby weakened locally so that the hybrid castingpart may at least partly loosen from the metallic part.

In view thereof, the technical problem underlying the present inventionis to develop a stirrer organ of the species mentioned hereinabove insuch a manner that the drawbacks outlined hereinabove are avoided.

This task is inventively solved in that the anchoring element isprovided with a perforated plate which is spot-wise fastened to themetallic part and which is arranged at least partly at a small distanceto the surface of the metallic part so as to configure the at least oneback-cutting.

In this manner, the contact face between the hybrid casting and theanchoring element is markedly increased as compared with prior art.Hazardous stress peaks are thus avoided. Furthermore, the quantity ofgrouted mineral cast can be reduced to a minimum in this manner.

As the planar anchoring element is arranged closely along the surface ofthe metallic part, the hybrid cast rather resembles a coating whichdependent on its viscosity can be cast-on or trowelled-on, with a hybridcast having a relatively high viscosity being preferably trowelled-on.Moreover, the perforated plate takes a stabilizing and reinforcingeffect in the entire casting body, so that the compound bonding of theinventive stirrer organ is markedly improved as compared with prior art.The portion of the load-bearing metallic part in the compound bonding,too, can be substantially enhanced without exceeding the given compositecomponent thickness.

Now, therefore, the present invention advantageously extends the rangeof application of the hybrid casting technology to older, existingstirrer organs made of steel which are severely attacked by the media tobe stirred. As a result hereof, these stirrer organs have to be replacedfrequently, which particularly involves an extensive spare parts stockkeeping.

Thanks to the present invention, it is now possible to rehabilitateattacked, metallic stirrer organs at low cost. For this purpose, damagedstirrer organs are cleaned or ground-off, provided with a perforatedplate, and subsequently the protective hybrid cast is cast-on ortrowelled-on. Initial tests have demonstrated that stirrer organsrehabilitated in this manner achieve a service life which issubstantially longer than it were in their new status. Maintenanceintervals for stirrer organs are enhanced, and spare parts stock keepingcan be omitted.

The inventive use of the perforated plate is not confined to planarmachinery components. It is also feasible to produce or rehabilitatecomposite components having a more complex geometry by covering thesurface of the metallic part, for example, with a plurality of smallerperforated plates arranged like a patchwork.

An advantageous embodiment of the present invention provides forfastening the perforated plate indirectly via spacer pieces to themetallic part and arranging it by means of the spacer pieces partly at asmall distance to the surface of the metallic part. The spacer piecesare preferably designed and built as washers, thus representing a simpleand low-cost measure. In a particularly preferable manner, the distancepieces are fastened to the metallic part by applying the spot weldingtechnique. This joining method can be performed quickly andcost-efficiently on the one hand, while the material properties of themetal are hardly altered by the short-term and spot-like thermal load onthe other hand.

According to an alternative advantageous embodiment of the presentinvention, the perforated plate is directly fastened at fastening pointsto the metallic part by applying the spot welding technique, theperforated plate being arched away from the metallic part in at leastone area between the fastening points and thus arranged partly at asmall distance to the surface of the metallic part. According to thisconfiguration, a use of spacer pieces can be dispensed with. Hereby itis possible to reduce the quantity of required hybrid cast to a minimum.

In accordance with a further advantageous embodiment of the presentinvention, the thickness of the perforated plate ranges between 0.2 and2 mm. The relevant choice of thickness can be adapted individually tothe relevant intended purpose of application. These plate thicknessesare already sufficient to achieve the afore-mentioned effect. Moreover,thin plates of this type are easy to process. The distance between theperforated plate and the surface of the metallic part preferablycorresponds roughly to 1.5 times to double the thickness of theperforated plate. In practice it has been demonstrated that a distancewithin this interval is absolutely sufficient to fill-up a load-bearingcasting underneath the perforated plate.

As the hybrid cast is quite tenacious, the perforated plate must have ahigh passage relative to the surface so as to allow it to be well flownthrough. This property is obtained by a perforated plate according toDIN 24 042 Form Qg, i.e. a perforated plate with a quadratic perforationin straight rows, wherein the distance of the quadratic holes stands ina certain relation to the dimensioning of the holes. Moreover, awide-meshed perforated plate of this type causes less target points ofrupture in the mineral casting layer than a close-meshed braiding.

The task outlined hereinabove is furthermore solved by applying a methodof the initially mentioned type by taking the following steps:

-   a) the damaged areas of the metallic stirrer organ are cleaned or    abraded;-   b) spacer pieces are fastened on the metallic stirrer organ;-   c) a perforated plate is so fastened at the spacers that it extends    at a small distance to the surface of the metallic stirrer organ in    the cleaned area and/or in the area of the abrasion;-   d) in the area of the perforated plate a hybrid casting is cast-on    or trowelled-on to the metallic stirrer organ so as to create a    rehabilitated stirrer organ in composite construction.

The damaged areas of the metallic stirrer organ are preferablyground-off. The spacer pieces to be affixed to the metallic stirrerorgan and/or the perforated plate to be affixed to the spacer pieces arepreferably fastened by applying the spot welding technique.

According to the present invention, the task outlined hereinabove isalternatively solved by applying a method of the initially mentionedtype by taking the following steps:

-   a) the damaged areas of the metallic stirrer organ are cleaned or    abraded;-   b) a perforated plate is directly affixed to the metallic stirrer    organ at the fastening points by applying the spot welding    technique;-   c) at least in one area between the fastening points, the perforated    plate is so bent away from the metallic stirrer organ to form at    least one arch that in the cleaned area and/or in the area of the    abrasion the perforated plate extends at a small distance to the    surface of the metallic stirrer organ;-   d) in the area of the perforated plate a hybrid casting is cast-on    or trowelled-on to the metallic stirrer organ so as to create a    rehabilitated stirrer organ in composite construction.

Here, too, the damaged areas of the metallic stirrer organ arepreferably ground-off.

In accordance with the methods described hereinabove, it is possible toproduce a rehabilitated stirrer organ in composite construction that maybe configured according to one of the embodiments described hereinabovein connection with the stirrer organ in composite construction or in anyarbitrary combination of the same.

A practical example of the present invention is more preciselyelucidated based on the following figures, wherein:

FIG. 1: shows a practical example for an inventive stirrer organ; and

FIG. 2: shows a cross-section of the practical example shown in FIG. 1along the line I-I.

FIG. 1 shows a top view onto a practical example for the inventivestirrer organ 1 in composite construction. According to this embodiment,the stirrer organ 1 is comprised of three stirrer blades 2 which areconnected to each other via a hub 3. Via the hub 3, the stirrer organ 1is connectible to a shaft not shown here, via which the stirrer organ 1can be moved in the plane of the blade.

FIG. 2 shows a cross-section of the practical example shown in FIG. 1along the line I-I. Hence, it represents a cross-section through astirrer blade 2 of stirrer organ 1.

The stirrer blade 2 is comprised of a metallic part 4, which aperforated plate 5 is spot-wise fastened to and which is thus retainedat a small distance to the surface of the metallic part 4 to configureback-cuttings. At the upper side of the metallic part 4, the perforatedplate 5 is affixed via spacer pieces 6 to the metallic part 4. At thelower side of the metallic part 4, the perforated plate 5 is directlyaffixed to the metallic part 4 at fastening points 7 by applying thespot welding technique. Between the fastening points 7, the perforatedplate 5 has been bent away from the metallic part 4 to configure arches8 so that the perforated plate 5 in these areas is kept at a smalldistance to the surface of the metallic part 4 to configureback-cuttings.

In accordance with alternative embodiments, the perforated plate 5 canbe fastened to the metallic part 4 exclusively indirectly via spacerpieces 6 or exclusively directly at fastening points 7.

The perforated plate 5 serves as anchoring element to anchor the hybridcasting 9 at the metallic part 4. When the perforated plate 5 has beenfastened to the metallic part 4, this compound structure comprised ofthe perforated plate 5 and the metallic part 4 is cast around with ahybrid cast or the hybrid cast is trowelled-on accordingly so that partof the hybrid cast reaches through the non-shown holes in the perforatedplate 5 and mainly completely fills the space between the perforatedplate 5 and the metallic part 4. By way of the subsequent age-hardeningof the hybrid cast, the hybrid casting 9 is formed which reaches throughthe holes of the perforated plate 5 and which reaches behind those areasof the perforated plate 5 not provided with holes and forming theinventive back-cuttings.

The practical example described based on these figures serves forexplanatory purposes and is non-restrictive.

1. Stirrer organ (1) in composite construction comprised of a metallicpart (4) and a hybrid casting (9), with the hybrid casting (9) beingfixed to the metallic part (4) by means of at least one anchoringelement which forms at least one back-cutting in the hybrid casting (9),wherein the anchoring element is provided with a perforated plate (5)which is spot-wise fastened to the metallic part (4) and which isarranged at least partly at a small distance to the surface of themetallic part (4) so as to configure the at least one back-cutting. 2.Stirrer organ (1) according to claim 1, wherein the perforated plate (5)is fastened to the metallic part (4) indirectly via spacer pieces (6)and that it is arranged by means of the spacer pieces (6) partly at asmall distance to the surface of the metallic part (4).
 3. Stirrer organ(1) according to claim 2, wherein the spacer pieces (6) are designed andbuilt as washers.
 4. Stirrer organ (1) according to claim 2, wherein thespacer pieces (6) are fastened to the metallic part (4) by applying thespot welding technique.
 5. Stirrer organ (1) according to claim 1,wherein the perforated plate (5) is indirectly fastened to the metallicpart (4) at fastening points (7) by applying the spot welding technique,the perforated plate (5) being arched-away from the metallic part (4) inat least one area between the fastening points (7), thus being partlyarranged at a small distance to the surface of the metallic part (4). 6.Stirrer organ (1) according to claim 1, wherein the thickness of theperforated plate (5) ranges between 0.2 and 2 mm.
 7. Stirrer organ (1)according to claim 6, wherein the small distance between the perforatedplate (5) and the surface of the metallic part (4) roughly correspondsto 1.5 times to double the thickness of the perforated plate (5). 8.Stirrer organ (1) according to claim 1, wherein the perforated plate (5)has a quadratic perforation in straight rows.
 9. Stirrer organ (1)according to claim 1, wherein the hybrid cast is applied by casting-onor trowelling-on.
 10. Method for rehabilitating a damaged, metallicstirrer organ, comprising the following steps: a) the damaged areas ofthe metallic stirrer organ are cleaned or abraded; b) spacer pieces (6)are fastened on the metallic stirrer organ; c) a perforated plate (5) isso fastened at the spacer pieces (6) that it extends at a small distanceto the surface of the metallic stirrer organ in the cleaned area and/orin the area of the abrasion; d) in the area of the perforated plate (5)a hybrid casting (9) is cast-on or trowelled-on to the metallic stirrerorgan (1) so as to create a rehabilitated stirrer organ (1) in compositeconstruction.
 11. Method according to claim 10, wherein the damagedareas of the metallic stirrer organ are ground-off.
 12. Method accordingto claim 10, wherein the spot welding technique is applied to fasten thespacer pieces (6) to the metallic stirrer organ and/or to fasten theperforated plate (5) to the spacer pieces (6).
 13. Method forrehabilitating a damaged, metallic stirrer organ, comprising thefollowing steps: a) the damaged areas of the metallic stirrer organ arecleaned or abraded; b) a perforated plate (5) is directly affixed to themetallic stirrer organ at the fastening points (7) by applying the spotwelding technique; c) at least in one area between the fastening points(7), the perforated plate (5) is so bent away from the metallic stirrerorgan to form at least one arch (8) that in the cleaned area and/or inthe area of the abrasion the perforated plate (5) extends at a smalldistance to the surface of the metallic stirrer organ; d) in the area ofthe perforated plate (5) a hybrid casting (9) is cast-on or trowelled-onto the metallic stirrer organ so as to create a rehabilitated stirrerorgan (1) in composite construction.
 14. Method according to claim 13,wherein the damaged areas of the metallic stirrer organ are ground-off.